1. Field of the Invention
The present invention relates to real-time object (RTO) graphics systems and, in particular, discloses a pipeline structure for the preprocessing of object fragment data used for calculating an image to be displayed.
2. Description of the Related Art
Graphics systems in common use normally utilize many different co-ordinate systems in the display of images. The fundamental co-ordinate system is the world co-ordinate system which includes all possible displayable co-ordinates. A second co-ordinate system is the viewing or window co-ordinate system which is used for locating a position or location on a display device such as a screen or printer. A viewing coordinate system is normally forms a `view port` or `window` of a certain portion of the world co-ordinate system. Methods of transforming a window coordinate system to its corresponding world co-ordinate system are well known in the art.
Graphic objects used in the display of images, often consist of many different instances of a collection of sub-objects. Each of these sub-objects is normally defined by a further relative co-ordinate system, with the position, scaling, rotation etc. of the sub-object defined relative to an overall position of the object. The use of a relative coordinate system allows the corresponding graphic objects to be easily manipulated through such processes as scaling, translation, coping and rotation. The use of relative co-ordinate systems are well known in the art.
When it comes time to display the objects falling within a certain widow or view port on a graphics display device, a determination must be made of which object, or part thereof, falls within the window or view port, and what shape that object will take upon consideration of the transformations required between the world, viewing and relative coordinate systems. The display of graphic objects is therefore normally achieved by applying the transformation to each object and `clipping` or culling those objects or portions thereof that lie outside the window or view port.